Apparatus and method of operating an audio system

ABSTRACT

An audio system includes a level controller receiving an input audio signal from an audio medium. The level controller includes a gain adjust module producing an output audio signal based on the input audio signal. A filter arrangement is communicatively coupled to the level controller. The filter arrangement receives the output audio signal and divides the output signal into a plurality of filtered signals. Each of the filtered signals corresponds to a respective frequency band. A multiband dynamics controller is communicatively coupled to the filter arrangement. The multiband dynamics controller receives the filtered signals and applies a respective gain characteristic to each of the filtered signals to thereby produce a plurality of gain adjust signals. The gain adjust signals are combined into a multiband dynamics controller output signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/316,689, filed on Dec. 17, 2008—now U.S. Pat. No. 8,204,258—, thedisclosure of which are hereby incorporated by reference in theirentirety for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the improvement of soundcharacteristics in an audio system.

2. Description of the Related Art

Various techniques have been developed to enhance the perceived qualityof audio signals. One of these techniques is dynamic range compression(DRC), which is a process that manipulates the dynamic range of an audiosignal. Compression may be used during broadcasting in order to alterthe perceived volume of audio.

Compression may be achieved by use of a compressor, which is sometimesreferred to as an automatic volume control. Compression may reduce thelevel of loud sounds over a certain threshold, while the level of quietsounds is not reduced. Thus, compression may reduce the dynamic range ofan audio signal. Compression may be performed to improve aesthetics ofthe sound, to accommodate technical limitations of audio equipment, orto improve the audibility of audio signals in noisy environments.

Quiet sounds may be overpowered in a noisy environment, making themdifficult to hear. That is, the background noise can drown out quietsounds. Reducing the sound level for loud sounds may result in the quietsounds being inaudible. Conversely, increasing the sound level for quietsounds may result in the loud sounds being uncomfortably loud.Compression may be used to make both the quiet and loud parts of anaudio signal audible at a comfortable level at the same time.Compression reduces the level of the loud sounds, but does not reducethe level of the quiet sounds. Thus, the sound level may be raised suchthat the quiet sounds are audible, but the loud sounds are not too loud.

The length of time required for a compressor to respond to changes ininput level is known as attack time. The length of time required for thesound level to fall from a maximum level to a steady state level isreferred to as decay time. The length of time the audio level remains atthe steady state level is referred to as the hold time. The length oftime required for a compressor to return to no gain reduction after theinput level falls below a steady state or threshold level is known asrelease time. In many compressors, the use may adjust the attack andrelease times. Some compressors, however, have fixed attack and releasetimes that are determined by the circuit design and that cannot beadjusted by the user. In some cases, the attack and release times are“automatic” or “program dependent.” That is, the times change dependingupon the input signal. The loudness pattern of the source material maybe modified by the compressor, the compressor may change the characterof the signal in very noticeable ways under certain settings.

Accordingly, what is neither anticipated nor obvious in view of theprior art is an improved apparatus and method of source level matchingboth when operating within a single audio medium and when switchingbetween audio media.

SUMMARY OF THE INVENTION

One embodiment of the multiband audio dynamics processor of the presentinvention has three main elements, including an automatic level control(ALC), a multiband filter, and a multiband dynamics controller. The ALCsection may reduce the difference in level between the loudest andquietest audio sources. By using a “slow” root mean square (RMS)detector, the long term RMS level is monitored and maintained, therebyallowing fast transients to remain. This helps to maintain the dynamicsof the source. A control signal is also output in order to freeze orhold the gain setting of the multiband dynamics controller when theinput falls below a specified threshold.

The multiband filter section may divide the input source into multiplefrequency ranges. In one embodiment, four frequency bands and firstorder filter sections are utilized. In a particular embodiment, thefirst band (B1) is 0-100 Hz, the second band (B2) is 100 Hz-600 Hz, thethird band (B3) is 600 Hz-4 kHz, and the fourth band (B4) is 4 kHz-20kHz and over. The filter types chosen may allow for seamless recombiningfor a flat frequency response (+/−0.1 dB).

The multiband dynamics controller may apply audio source-derived gainadjustments on a band-by-band basis. The RMS detector elements of themultiband dynamics controller may respond and apply gain adjustmentsmuch more quickly than RMS detector elements located within the ALC.Each band may have independently adjustable RMS tables, attack, decay,and hold times. Because most of the energy below 100 Hz is monotone innature, the left/right bands are summed and controlled together in orderto increase efficiency. The gain applied to the individual bands is afunction of the input signal, the status of the freeze/hold signal, therespective bands' RMS table output, and the gain pullback control. Ifthe post ALC signal level falls below the specified threshold, the lastRMS table output (Gain value) will be held until this level exceeds thethreshold value. This is done to prevent abrupt gain changes duringquiet music passages. RMS table output gain values are a function of theinput levels of their respective bands and the compressorcharacteristics assigned to them. The B2 and B3 bands for the left andright channels are summed together in order to create the signal used tocontrol the pullback function. The pullback function is required inorder to prevent overload of the output signal that may result when theindividual bands are summed back together to recreate the full audiospectrum left/right channels.

The present invention may provide source level matching both insituations where audio is sourced from two different types of audiomedia and in situations where a single type of audio medium providesmultiple sources of audio. Source levels for a given source (e.g., acompact disc) can vary significantly, and thus source level matching isbeneficial. Improved source level matching with an automatic levelcontrol function reduces the need for the end user to adjust the volumein response to switching between different sources. This may beespecially advantageous in higher noise environments such as anautomobile, or when using a portable audio player and wearingheadphones.

The multiband dynamics controller may provide two primary functions. Oneof the functions is to apply a dynamic, source-dependent equalization.The other of the functions is to increase the energy density of theoutput signal at higher levels (e.g., frequency levels). The result is amore powerful sound characteristic. This second function may beapplicable to automotive and portable audio player markets.

The invention comprises, in one form thereof, an audio system includingan automatic level controller receiving at least one input audio signalfrom at least one audio medium. The automatic level controller includesa gain adjust module for producing an output audio signal based on theat least one input audio signal. A difference between a maximum soundlevel and a minimum sound level of the at least one input audio signalis greater than a difference between a maximum sound level and a minimumsound level of the output audio signal. A filter arrangement iscommunicatively coupled to the automatic level controller. The filterarrangement receives the output audio signal and divides the outputsignal into a plurality of filtered signals. Each of the filteredsignals corresponds to a respective frequency band. A multiband dynamicscontroller is communicatively coupled to the filter arrangement. Themultiband dynamics controller receives the filtered signals and appliesa different respective gain characteristic to each of the filteredsignals to thereby produce a plurality of gain adjust signals. The gainadjust signals are combined into a multiband dynamics controller outputsignal.

The invention comprises, in another form thereof, a method of operatingan audio system, including receiving at least one input audio signalfrom at least one audio medium. An output audio signal is produced basedon the at least one input audio signal. A difference between a maximumsound level and a minimum sound level of the at least one input audiosignal is greater than a difference between a maximum sound level and aminimum sound level of the output audio signal. The output signal isdivided into a plurality of filtered signals. Each of the filteredsignals corresponds to a respective frequency band. A differentrespective gain characteristic is applied to each of the filteredsignals to thereby produce a plurality of gain adjust signals. A valueof the gain characteristic is held constant so long as a level of theoutput audio signal is below a threshold value. The gain adjust signalsare combined into a controller output signal.

The invention comprises, in yet another form thereof, an audio systemincluding an automatic level controller for receiving at least one inputaudio signal from at least one audio medium. The automatic levelcontroller includes a gain adjust module for producing an output audiosignal based on the at least one input audio signal. A differencebetween a maximum sound level and a minimum sound level of the at leastone input audio signal is greater than a difference between a maximumsound level and a minimum sound level of the output audio signal. Athreshold detector module is communicatively coupled to the gain adjustmodule and receives the output audio signal. The threshold detectormodule transmits a gate control signal when the output audio signalfalls below a predetermined threshold value. A filter arrangement iscommunicatively coupled to the automatic level controller. The filterarrangement receives the output audio signal and divides the outputaudio signal into a plurality of filtered signals. Each of the filteredsignals corresponds to a respective frequency band. A multiband dynamicscontroller is communicatively coupled to the filter arrangement. Themultiband dynamics controller receives the filtered signals and appliesa different respective gain characteristic to each of the filteredsignals to thereby produce a plurality of gain adjust signals. Themultiband dynamics controller also receives the gate control signal andlimits at least one of the gain adjust signals to a maximum value inresponse to receiving the gate control signal. The gain adjust signalsare combined into a multiband dynamics controller output signal by themultiband dynamics controller.

An advantage of the present invention is that it produces a morepowerful sound characteristic than known methods.

Another advantage is that the present invention may reduce the need forthe end user to adjust the volume when the audio system switches betweendifferent sources.

Yet another advantage is that the present invention reduces noise in theaudio output.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and objects of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a block diagram of one embodiment of a multiband audiodynamics processor of the present invention;

FIG. 2 is a block diagram of the automatic level control of themultiband audio dynamics processor of FIG. 1;

FIG. 3 is an exemplary plot of RMS output level versus RMS input levelfor the automatic level control of the multiband audio dynamicsprocessor of FIG. 1;

FIG. 4 a is a block diagram of the left channel of the multiband filterof the multiband audio dynamics processor of FIG. 1;

FIG. 4 b is a block diagram of the right channel of the multiband filterof the multiband audio dynamics processor of FIG. 1;

FIG. 5 is a plot of the fast RMS frequency response of the multibandfilter of the multiband audio dynamics processor of FIG. 1;

FIG. 6 is a block diagram of the multiband dynamics controller of themultiband audio dynamics processor of FIG. 1;

FIG. 7 is an exemplary plot of RMS output level versus RMS input levelfor the compressor of the multiband audio dynamics processor of FIG. 1;

FIG. 8 a is an exemplary plot of a prior art output audio signal;

FIG. 8 b is an exemplary plot of an output audio signal of the multibandaudio dynamics processor of FIG. 1;

FIG. 9 illustrates exemplary plots of the energy versus frequency for anoutput audio signal of the multiband audio dynamics processor of FIG. 1and for a prior art output audio signal;

FIG. 10 is a flow chart of one embodiment of a method of the presentinvention for operating an audio system.

DETAILED DESCRIPTION

The embodiments hereinafter disclosed are not intended to be exhaustiveor limit the invention to the precise forms disclosed in the followingdescription. Rather the embodiments are chosen and described so thatothers skilled in the art may utilize its teachings.

Referring now to the drawings, and particularly to FIG. 1, there isshown one embodiment of a multiband audio dynamics processor 20including an automatic level controller (ALC) 22, multiband filters 24,and multiband dynamics controller (MDC) 26. An audio signal in the formof a source input 28 may be received by ALC 22. Source input 28 may befrom a radio, compact disc (CD) player, or other audio signal medium.The medium from which source input 28 is sourced may vary with time.That is, the user may manually switch the audio system between radio andCD player, or the audio system may automatically switch itself betweenradio and CD player. ALC 22 may reduce the difference in sound levelbetween the loudest and quietest audio sources. ALC 22 may outputanother audio signal 30 having adjusted sound levels. Output signal 30from ALC 22 may be received by multiband filters 24.

Multiband filters 24 may divide ALC output signal 30 into multiplefrequency bands, each of which may be associated with a certain type ofsound generator that may typically produce the sounds present in signal30. That is, various generators of sound, such as a human voice andvarious types of musical instruments, such as strings, horns,percussion, etc., may produce sounds predominantly within certainfrequency bands. Multiband filters 24 may divide ALC output signal 30into frequency bands that each correspond to the frequencies produced bya respective producer of sounds found in signal 30. Multiband filter 24may output yet another audio signal 32 that has adjusted sound levelsand that is divided into multiple frequency bands. Thus, audio signal 32may actually be in the form of multiple signals, each corresponding to arespective on of the frequency bands. Output signal(s) 32 from multibandfilters 24 may be received by MDC 26.

MDC 26 may apply a different gain value to each of the bands of signal32. ALC 22 may transmit a gate control signal 34 to MDC 26 that preventsthe gain values from exceeding a maximum value when the input audiosignal falls below a predetermined threshold value. MDC 26 produces afinal output audio signal 36 that may be received by speakers of theaudio system.

ALC 22 is shown in more detail in FIG. 2. ALC 22 includes Left/RightDetect Logic 38, Look Ahead Delay 40, RMS Detector Gain Table 42, ALCGain Adjust module 44, and Gate Threshold Detector module 46. Left/rightdetect logic 38 transmits a left/right detect audio signal 48 to RMSDetector Gain Table 42. The long term RMS level may be monitored andmaintained by use of a “slow” RMS detector. The use of the slow RMSdetector may allow fast transients to remain and enable the dynamics ofthe source to be maintained. The output of RMS Detector Gain Table 42may be an ALC Gain control signal 50 that may apply different gainvalues to the left and right channels.

ALC Gain control signal 50 is received by ALC Gain Adjust 44. ALC GainAdjust 44 also receives a left/right delayed audio signal 52 from LookAhead Delay 40. ALC Gain Adjust 44 transmits ALC output signal 30 tomultiband filters 24. ALC output signal 30 is also received by GateThreshold Detector 46.

Gate Threshold Detector 46 outputs gate control signal 34 to MDC 26.Gate control signal 34 freezes or holds the gain setting of MDC 26 whenALC output signal 30 falls below a specified or predetermined threshold.

An exemplary plot of the RMS output level of ALC 22 as a function of theRMS input level is plotted in FIG. 3.

As shown in FIGS. 4 a and 4 b, Multiband Filters 24 may divide each ofthe left and right input sources into multiple frequency ranges by useof lowpass filters 54, 56, 58, inverters 60, 62, 64 and adders 66, 68,70. The specific embodiment of the portion of Multiband Filters 24 thatdivides the left input source into multiple frequency ranges isillustrated in FIG. 4 a. Lowpass filters 54, 56, 58 have cutofffrequencies of 600 Hz, 4000 Hz and 100 Hz, respectively, resulting inoutput B4LOut 72 having a passband of 4000 Hz and above, output B3LOut74 having a passband of 600 Hz to 4000 Hz; output B2LOut 76 having apassband of 100 Hz to 600 Hz; and output B1LOut 78 having a passband of0 Hz to 100 Hz. In general, the passbands may be selected such that eachpassband contains at least one frequency of interest or range offrequencies of interest. For example, the passband of 100 Hz to 600 Hzincludes frequencies of the human voice; the passband of 600 Hz to 4000Hz includes frequencies of particular types of musical instruments, suchas horn or strings, etc. In another embodiment (not shown), themultiband filters divide the input source into five passbands, includinga first passband from 0 Hz to 100 Hz; a second passband from 100 Hz to600 Hz; a third passband from 600 Hz to 2500 Hz; a fourth passband from2500 Hz to 10,000 Hz; and a fifth pass band of 10,000 Hz and above. Thefifth passband may include the frequencies of musical instruments suchas cymbals and synthesizers.

The portion of Multiband Filters 24 that divides the right input sourceinto multiple frequency ranges is illustrated in FIG. 4 b and issubstantially similar to the portion described with reference to FIG. 4a. Thus, the portion shown in FIG. 4 b will not be described in detailherein in order to avoid repetition.

FIG. 5 illustrates plots of the RMS frequency response for each of theoutputs B1LOut, B2LOut, B3LOut, and B4LOut of FIG. 4 a. The respectivepassbands of these outputs are evident in the plots. Also plotted is theconstant summed response of the four filters taken as a whole. Thefilter types may be chosen such that the filters can be seamlesslyrecombined to produce a flat frequency response. In one embodiment, thecombined frequency response does not deviate more that 0.1 dB in eitherdirection.

A more detailed block diagram of MDC 26 is illustrated in FIG. 6. Aseparate RMS Detector Table 80 ₁₋₄ is provided for each of the fourbands. RMS Detector Tables 80 each define a respective RMS detector andcompressor. Detector Tables 80 may control the attack and release of thecompressors. The outputs 32 of Multiband Filters 24 are received by RMSDetector Tables 80 as well as by Gain Adjusts 82 ₁₋₄. These RMSdetectors and Gain Adjusts may respond and apply gain adjustments morequickly than those located within ALC 22.

Hold blocks 84 ₁₋₄ provide hold times and thus prevent the compressorsfrom reducing the outputs to the level of noise, sometimes referred toas “digging to the noise floor.” A different hold period may be providedfor each frequency band, which may involve a subjective optimization.Each hold time may be dependent upon the threshold level of therespective compressor.

A typical response curve of one or more of the compressors isillustrated in FIG. 7. At the upper end of the curve, the curve becomesnon-linear, i.e., at approximately −15 dB. Thus, in the illustratedembodiment, the RMS input threshold level of each compressor is about−15 dB. Moreover, the response curve for the three lower frequency bandsdeviates at 86 from the response curve for the highest frequency band at88. Although the compressor curve of FIG. 7 is also non-linear at RMSinput levels of −69 dB and below, this is non-linearity at the lower endis not present in all embodiments of the present invention.

Each of the frequency bands may correspond to a different respectivegain characteristic. Further, each of the frequency bands may correspondto a different respective attack time and a different respective decaytime.

Because most of the energy in the lowest frequency band (i.e., below 100Hz) is monotone in nature, the left and right bands may be summed andcontrolled together in order to make multiband audio dynamics processor20 more efficient. Although not shown in the drawings, this summing mayoccur between multiband filters 24 and MDC 26.

Gain pullback control and/or feedback may be provided by Pullback RMSDetector Table module 90 (FIG. 6). An output 92 of Pullback RMS DetectorTable 90 is multiplied with each of outputs 94 ₁₋₄ of RMS DetectorTables 80 ₁₋₄ at multipliers 96 ₁₋₄. Outputs 98 ₁₋₄ of multipliers 96₁₋₄ are received by hold blocks 84 ₁₋₄. Outputs 100 ₁₋₄ of hold blocks84 ₁₋₄ are received by respective gain adjusts 82 ₁₋₄. Thus, the gainapplied to the individual bands by gain adjusts 82 ₁₋₄ is a function ofinput signal 32, the status of freeze/hold signal 100, the respectivebands' RMS Detector Table output 94, and the output 92 of Pullback RMSDetector Table 90.

If output 30 of ALC 22 falls below the specified threshold, then themost recent output 94 of RMS Detector Table 80 (i.e., the most recentgain value) may be held until output 30 of ALC 22 exceeds the specifiedthreshold. This holding constant of the gain value while the ALC signalis below the threshold value may prevent abrupt gain changes duringquiet music passages. RMS table output gain values 94 may be a functionof the input levels as represented by signals 32 of their respectivefrequency bands and of the compressor characteristics defined by the RMSDetector Tables 80.

Output signals 102 ₂ and 102 ₃ of Gain Adjusts 82 ₂ and 82 ₃,respectively, for the second and third frequency bands may be summedtogether at 104 in order to create a summed signal 106 received byPullback RMS Detector Table 90 and used for controlling the pullbackfunction. The outputs of only two Gain Adjusts 82 ₂ and 82 ₃ of the fourGain Adjusts 82 ₁₋₄ may be used as inputs to Pullback RMS Detector Table90 because frequency bands B2 and B3 may have the most energy. PullbackRMS Detector Table 90 may function to prevent the output from going overscale by preventing the gain from becoming too high in an uncontrolledmanner. The pullback function may prevent overload of final output audiosignal 36 that may result when individual frequency bands B1-4 aresummed back together at 108 to recreate the full audio spectrumleft/right channels. Specifically, Pullback RMS Detector Table 90 maydetermine whether the sum of output signals 102 ₂ and 102 ₃ of GainAdjusts 82 ₂ and 82 ₃ exceeds a threshold value.

MDC 26 may serve the function of applying a dynamic, source dependentequalization. MDC 26 may also increase the energy density of outputsignal 36 at times when the energy density of output signal 36 isrelatively low. This functions performed by MDC 26 may result in a morepowerful sound characteristic and may be applicable to both automotiveaudio systems and portable audio players.

The present invention may provide source level matching for a singlemedia type as well as for different media types. Source levels for agiven source, such as a CD player, can vary significantly, and thus maybenefit from source level matching. The present invention may provide animproved method of source level matching with an automatic level controlfunction that reduces the need for the end user to adjust the volume ofdifferent audio sources. Reducing the need for the user to adjust thevolume may be especially beneficial in higher noise environments such asautomobiles, or when the user is wearing headphone and his ears arethereby vulnerable to sudden increases in sound volume.

The overall effect of the present invention on the output signal isillustrated via a comparison of FIGS. 8 a and 8 b. FIG. 8 a is anexemplary plot of a prior art output signal having a Peak value and anRMS value as shown. FIG. 8 b is an exemplary plot of an output signalachieved by use of the present invention. The plot of FIG. 8 b also hasa Peak value and an RMS value. However, the ratio of RMS value to Peakvalue in FIG. 8 b is higher than is the ratio of RMS value to Peak valuein FIG. 8 a. The average of the output signal may also be a higherpercentage of the Peak value as a result of the present invention. Asthe result of the present invention, a listener's perception may be thatthe sound is much louder and/or bigger.

The present invention may also have the effect of lengthening the timebetween adjacent peaks (i.e., local maximums) and between adjacentvalleys (i.e., local minimums) in the output signal. For example, a timeduration 110 between adjacent valleys of the output signal of thepresent invention is longer than a time duration 112 between adjacentvalleys of the prior art output signal.

Another illustration of the overall effect of the present invention onthe output signal is presented in the energy versus frequency plot ofFIG. 9. The output signal of the present invention has a lower peak ormaximum energy than does the prior art output signal, but the energy atthe lower frequencies and upper frequencies is higher with the presentinvention. As a result, the overall energy of the output signal, i.e.,the integration of the area under the curve in FIG. 9, is greater withthe present invention than with the prior art.

One embodiment of a method 1000 of the present invention for operatingan audio system is illustrated in FIG. 10. In a first step 1010, atleast one input audio signal is received from at least one audio medium.For example, an input audio signal in the form of a source input 28(FIG. 1) may be received by ALC 22. Source input 28 may be from a radio,compact disc (CD) player, or other audio signal medium, for example.

In a next step 1020, an output audio signal is produced based on the atleast one input audio signal, a difference between a maximum sound leveland a minimum sound level of the at least one input audio signal beinggreater than a difference between a maximum sound level and a minimumsound level of the output audio signal. That is, an output audio signal30 may be output from ALC 22 with adjusted sound levels relative tosource input 28. Particularly, ALC 22 may reduce the difference in soundlevel between the loudest and quietest sections of source input 28 andoutput a resulting output audio signal 30.

Next, in step 1030, the output signal is divided into a plurality offiltered signals, each of the filtered signals corresponding to arespective frequency band. In the example illustrated in FIG. 4 a,multiband filters 24 divide output audio signal 30 into four bandpassfiltered signals 32 corresponding to frequency bands 0-100 Hz, 100Hz-600 Hz, 600 Hz-4000 Hz, and over 4000 Hz, respectively.

In step 1040, a different respective gain characteristic is applied toeach of the filtered signals to thereby produce a plurality of gainadjust signals. For example, within MDC 36, a different respectivecompressor curve (FIG. 7), i.e., gain characteristic, may be applied toeach of the four bandpass filtered signals 32 ₁₋₄ to thereby producegain adjust signals 102 ₁₋₄ (FIG. 6).

In a next step 1050, a value of the gain characteristic is held constantso long as a level of the output audio signal is below a thresholdvalue. That is, when output audio signal 30 is below a threshold value,gate threshold detector 46 (FIG. 2) outputs gate control signal 34,which freezes or holds the gain setting of MDC 26 so long as outputaudio signal 30 remains below the threshold value.

In a final step 1060, the gain adjust signals are combined into acontroller output signal. As shown in FIG. 6, gain adjust signals 102₁₋₄ are combined at 108 into a controller output signal 36.

As mentioned above, various numbers of compressor bands other than fouror five could be utilized with the present invention. Moreover, filtertypes other than as shown in multiband filters 24 could be utilized.Lastly, although the present invention is described herein asfunctioning primarily digitally, an analog equivalent is within thescope of the invention.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains.

1. A method of operating an audio system, the method comprising thesteps of: producing an output audio signal based on at least one inputaudio signal, a difference between a maximum sound level and a minimumsound level of the at least one input audio signal being greater than adifference between a maximum sound level and a minimum sound level ofthe output audio signal; separating the output signal into a pluralityof filtered signals, each of the filtered signals corresponding to arespective frequency band; applying a different respective gaincharacteristic to each of the filtered signals to thereby produce aplurality of gain adjust signals; and holding respective values of thegain characteristics substantially constant so long as a level of theoutput audio signal is below a threshold value.
 2. The method of claim 1wherein each of the gain characteristics is a function of a level of therespective filtered signal.
 3. The method of claim 1 comprising thefurther step of determining whether the output audio signal is below apredetermined threshold value.
 4. The method of claim 3 comprising thefurther step of adjusting at least one of the gain adjust signals basedupon whether the output audio signal is below the predeterminedthreshold value.
 5. The method of claim 1 wherein each of the frequencybands corresponds to a predominant frequency of a selected type ofmusical instrument.
 6. The method of claim 1 comprising the furthersteps of: receiving at least one of the gain adjust signals; andproviding feedback to reduce at least one of the gain adjust signals ifthe received gain adjust signal exceeds a threshold value.
 7. The methodof claim 1 comprising the further step of combining the gain adjustsignals into a controller output signal, and wherein the separating stepis performed via use of lowpass filters, invertors and adders.
 8. Anaudio system, comprising: an automatic level controller including: again adjust module configured to produce an output audio signal based onat least one input audio signal, a difference between a maximum soundlevel and a minimum sound level of the at least one input audio signalbeing greater than a difference between a maximum sound level and aminimum sound level of the output audio signal; and a threshold detectormodule communicatively coupled to the gain adjust module and configuredto receive the output audio signal, and transmit a gate control signalwhen the output audio signal falls below a predetermined thresholdvalue; a filter arrangement communicatively coupled to the automaticlevel controller, the filter arrangement being configured to receive theoutput audio signal and separate the output audio signal into aplurality of filtered signals, each of the filtered signalscorresponding to a respective frequency band; and a multiband dynamicscontroller communicatively coupled to the filter arrangement, themultiband dynamics controller being configured to: receive the filteredsignals and apply a different respective gain characteristic to each ofthe filtered signals to thereby produce a plurality of gain adjustsignals; and receive the gate control signal and limit at least one ofthe gain adjust signals to a maximum value in response to receiving thegate control signal.
 9. The audio system of claim 8 wherein each of thegain characteristics is a function of a level of the respective filteredsignal.
 10. The audio system of claim 8 wherein each of the frequencybands corresponds to a predominant frequency of a selected type ofmusical instrument.
 11. The audio system of claim 8 wherein themultiband dynamics controller is configured to combine the gain adjustsignals into a multiband dynamics controller output signal, themultiband dynamics controller including a pullback module configured toreceive at least one of the gain adjust signals and provide feedback toreduce at least one of the gain adjust signals if the received gainadjust signal exceeds a threshold value.
 12. The audio system of claim 8wherein the filter arrangement comprises a plurality of lowpass filters,a plurality of inverters, and a plurality of adders.
 13. The audiosystem of claim 8 wherein each of the frequency bands corresponds to adifferent respective attack time and a different respective decay time.